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<p>Thanks for the replies! This is very helpful. </p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Ardour-Users <ardour-users-bounces@lists.ardour.org> on behalf of Chris Caudle <chris@chriscaudle.org><br>
<b>Sent:</b> Wednesday, October 11, 2017 5:23 PM<br>
<b>To:</b> ardour-users@lists.ardour.org<br>
<b>Subject:</b> Re: [Ardour-Users] input levels, master levels</font>
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<div class="PlainText">On Fri, September 29, 2017 6:12 am, Matt Keys wrote:<br>
> question. What is the best practice regarding normalizing input volume<br>
> levels of unbalanced, balanced, and xlr (or a mix thereof) into ardour?<br>
<br>
Following up on what Seablade wrote a week or so ago, the basic principle<br>
is that all electronics have a minimum level of noise always present, and<br>
a maximum signal level that can be handled, both determined primarily by<br>
the circuit configuration (i.e. out of your control if you are not <br>
designing from scratch).<br>
A basic rule of thumb is that you want to apply as much gain as you can<br>
stand as early as possible for lowest noise build up, but you have to<br>
check that against maximum signal limits to make sure you do not introduce<br>
distortion if there is equipment in the middle or end of the chain which<br>
cannot handle signals as high as the first device in the chain.<br>
<br>
> guitar (unb TS) -><br>
<br>
Can cover a wide range of signal levels depending on whether you are<br>
playing single note lines, or hitting chords really hard. You may have to<br>
play around with this stage:<br>
> gfx (2x XLR) -><br>
<br>
to find the best compromise of noise and distortion levels.<br>
<br>
> analog mixer (2x balanced TS) -><br>
<br>
Check the maximum output level spec of the guitar effect and the maximum<br>
input level of the mixer. That may be given in logarithmic units,<br>
decibels. That relates to absolute levels in volts, but the short version<br>
is as long as the subscripts match you can compare directly. Watch out<br>
for different subscripts, which means different reference levels are used.<br>
So if the guitar effect gives it maximum output level in dBu, and the<br>
mixer lists the maximum input level in dBu, compare them directly. If<br>
for example the guitar unit lists output level in dBV and the mixer spec<br>
gives the maximum input level in dBu, you can't compare the values<br>
directly, you have to convert to the same reference level.<br>
<br>
The analog mixer likely has some kind of LED meters showing peak levels,<br>
but might not have on each channel. In that case you need to make sure<br>
you do not clip an intermediate stage in the mixer channel before it gets<br>
to the channel level control and the sum bus peak meter.<br>
<br>
I'll give a concrete example.<br>
Let's say your guitar FX unit says either max output level 20dBu, or<br>
something like nominal output 4dBu, 16dB headroom, which would be the same<br>
(+4 nominal +16 headroom = 20dBu).<br>
<br>
Let's say you look at your mixer spec and it says max input for line input<br>
is 18dBu. You would need to make sure the trim control on the mixer is at<br>
least at -2dB so that after the trim control the maximum signal coming to<br>
the mixer circuitry could be 20dB -2dB = 18dBu (assuming both devices give<br>
their levels in dBu).<br>
<br>
> usb audio interface<br>
<br>
Same thing, this time with the mixer max output levels and the audio<br>
interface max input levels. Depending on where the level control of the<br>
audio interface is in the circuit it may be better to run the mixer high<br>
and cut the levels at the audio interface, or cut back the output levels<br>
at the mixer, or maybe your audio interface is good quality and it can<br>
handle whatever level the mixer is capable of generating.<br>
<br>
> -> ardour<br>
<br>
Internally ardour is going to be a non-issue, the place where you have to<br>
watch is on the master output bus, because the audio data from there gets<br>
sent to the USB audio interface, and it can only handle up to 0dB FS (the<br>
FS meaning full scale, because that point the data is just abstract<br>
numbers, there is no physical reference yet like there is for the analog<br>
level standards that get labelled as dBu or dBV or even just as volts).<br>
<br>
Ardour has meters that will show you the peak level reached, make sure it<br>
never goes over 0 and you are OK on the ardour side. Hitting 0<br>
occasionally can be OK, I like to aim for lower because some equipment<br>
sounds a little strained as the distortion starts increasing if the levels<br>
are close to 0. Advanced topic for later, mixing to calibrated loudness<br>
level and not worrying about the levels as much. Don't worry about that<br>
yet, I just bring it up to point out you can ignore anyone who tells you<br>
that you "have to" get your mix to hit 0dB, or -0.1dB, or some other<br>
arbitrary number that is close to maxxed out, that is an anachronism left<br>
over from cassette tape days.<br>
<br>
> .. each point has volume adjust. Let's say I bypass any effects and I'm<br>
> 'clean' through to the usb mixer, but in ardour it sounds too<br>
> hot/distorted in master out.<br>
<br>
At that point you have to hope that your analog mixer is flexible enough<br>
that you can listen at various points along the signal chain and make sure<br>
it is still clean at each point. If your guitar efx unit has a headphone<br>
output, check to make sure it is clean at the effect unit. If the mixer<br>
has a pre-fader listen control, use that to route the guitar signal to the<br>
mixer output and make sure it is cleaning coming out of the mixer channel.<br>
If not, then turn down the output of the guitar unit, or turn down the<br>
input trim on the mixer channel, if that doesn't help you may be clipping<br>
the input of the guitar unit, try turning down the input gain on the<br>
guitar unit until you are sure that the signal coming through the mixer<br>
channel is clean. After that change from pre-fader listen back to normal<br>
routing and make sure it sounds OK at the output of the mixer (check the<br>
monitor speaker output of the mixer, or check with headphones, something<br>
that listens to the signal before it hits the A/D converter in the audio<br>
interface).<br>
<br>
If it is clean at that point then you just have the audio interface to<br>
worry about. When you route the signal to a track in ardour, watch the<br>
signal meters at the track, if the meters keep hitting 0dB then the signal<br>
is too high going into the audio interface, you need to either use the<br>
input level control of the interface, or the output level control of the<br>
mixer to keep peaks at around -3dB or so at max, lower is perfectly fine. <br>
Be sure to really wail on your guitar when you are checking, you don't<br>
want to just give it a little pluck and think you are good, only to find<br>
out that when you really get into playing you ruined a good take because<br>
you were playing harder than when you first set all the levels and<br>
something started distorting.<br>
<br>
Written out like this it sounds more complicated than it is, the process<br>
is just a little tedious the first couple of times, you just have to start<br>
at the beginning (i.e. the guitar connection) and work your way though the<br>
signal chain checking each step along the way. After you do it a couple<br>
of times it should come more easily.<br>
<br>
-- <br>
Chris Caudle<br>
<br>
<br>
<br>
<br>
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